1. Field of the Invention
The present invention relates to a method of forming a superconductor film. More specifically, the present invention relates to method of forming a superconductor film of a compound of magnesium and boron formed on a substrate by vacuum evaporation of magnesium and boron.
2. Description of the Related Art
A MgB2 compound features one of high transition temperature of any superconductor. It is reported that the coherent length ξ(0)=54 Å, magnetic penetration depth of MgB2 is 140-180 nm. A thin film of MgB2 can be integrated on a substrate to form an integrated circuit of a superconductor film of MgB2 at a high temperature. Thus the MgB2 film compound is expected to apply to electronics devices such as thin film devices.
One well known method of making the superconductor of MgB2 is to form a bulk of MgB2 by compression molding of powder of single crystals of MgB2 and then annealing the bulk at a high temperature. Another method of forming the superconductor of MgB2 is to form a thin film of a MgB2 compound by using PLD (pulse laser deposition), and then annealing the thin film of MgB2 in the temperature range of 600° C.-1200° C. to make the film superconductive. The PLD method focuses a pulsed laser beam on a boron target to evaporate boron atoms on a substrate. The boron atoms on the substrate are exposed to high temperature magnesium vapor in a reaction room to form the MgB2 film on the substrate. Further the film is annealed at a high temperature so as to be superconductive. Another method of forming the superconductor film of a MgB2 compound by using the PLD is as follows.
Magnesium atoms and boron atoms are deposited on a substrate by the PLD method. Moreover the atoms of magnesium and boron on the substrate are exposed to vapor of magnesium in the reaction room. The magnesium and boron on the substrate react in the magnesium vapor to form a thin film of the MgB2 compound on the substrate. Annealing the MgB2 film at a high temperature enables the film to have features of a superconductor.
All prior art regarding fabrication of the superconductor of the MgB2 compound requires high temperature annealing in the range of 600° C.-1200° C. The necessity of the annealing process of the MgB2 film to produce features of a superconductor makes fabrication of a device such as a thin film integrated circuit on a substrate difficult. Further, an as-grown film of MgB2 on a substrate by vacuum evaporation of magnesium and boron having characteristics of a superconductor without being annealed has not been realized at the present time.